Author Affiliations: Centre for Synthesis and Chemical Biology, Department of Pharmaceutical and Medicinal Chemistry, Royal College of Surgeons in Ireland, Dublin, Ireland (Dr Rooney); and Faculty of Health Sciences, Universidade de Brasilia, Brasilia, Brazil (Dr Dórea).
Shargorodsky et al1 investigated the association of heavy metals and hearing loss in adolescents; they reported no overall association between quartiles of blood mercury or urinary arsenic levels and hearing loss and found that urinary cadmium and blood lead levels were associated with substantially increased odds of high-frequency hearing loss. They state that the measurement of serum mercury levels is reflective of the “current body burden of the heavy metal as influenced by recent exposure.” As has been discussed previously,2 urine and serum mercury levels are reflective only of recent short-term exposure, not of historical, long-term, or low-dose mercury exposure. This limitation is in part attributable to the very long half-life of mercury in the brain. The authors go on to say, “Longer-term exposure would be better measured by mercury levels in hair.” Again, this statement is not strictly accurate: while hair mercury levels are known to be reflective of exposure to methyl-mercury from fish consumption, they are not reflective of elemental mercury exposure. It is also noteworthy that exposure to elemental, ethyl-mercury, and methyl-mercury (but, ironically, not inorganic mercury) can lead to deposition of inorganic mercury in the brain via the metabolism. However, the National Health and Nutrition Examination Survey collects data on diet, dental health, and vaccinations. Using these data, it should be possible to produce a mercury “exposure index” that might prove more valuable in analyzing the relationship between mercury exposure and hearing deficit.
Rooney JPK, Dórea JG. Hearing Loss in US Adolescents and Exposure to Heavy Metals: Mercury in Perspective. Arch Otolaryngol Head Neck Surg. 2012;138(6):608-609. doi:10.1001/archoto.2012.907